<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .outer {
            width: 100px;
            height: 100px;
            background: #000;
            border: 10px solid red;
            padding: 10px;
            margin: 10px;
            float: left;
        }

        .sky {
            width: 100px;
            height: 100px;
            background: green;
            float: left;

        }
        .blue {
            border: 10px solid pink;
            float: left;
        }
        .blue>div {
            width: 100px;
            height: 100px;
            background: blue;
            /* float: left; */
        }

        span{
            width: 100px;
            height: 100px;
            background: red;
            border: 10px solid black;
            padding: 20px;
            margin: 10px;
            /* display: block; */
            /* float: left; */
        }
    </style>
</head>
<body>
    <!-- 
    盒子的占位会有部分样式影响：内容、宽度、高度、边框、外边距与内边距
    行内元素：不支持宽高，支持边框、内外边距。
        变为块元素：
        1. 使用浮动
        2. 使用 display: block;其他取值包括：

     -->
    
     <div class="outer">
     </div>
     <div class="sky"></div>
     <div class="blue">
        <div>in blue</div>
     </div>
     <br/>
     <span>abc</span>
</body>
</html>